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Strangest problem I've ever had

Ok.
Bought a house.
Paid guy to run wires through the wall for a 3 point system.(too many obstacles & $$ for surround)

Have walls patched and painted. Moved in.
unpacked My Pride and joy B&K 7 channel.

system includes Onkyo sr705, HDMI from cable box to onkyo, connected polk rti12 speakers to B&K with bananas.

turned it all on, incredibly loud buzz snap crackle pop, onkyo shuts off and burnt wire smell fills the air.

Trouble shoot. all wires were hooked up right.
connect speaker wires directly to onkyo one at a time. the farthest one away in the wall shuts off onkyo. I run a new wire on the floor to that speaker. It works.

So it's the wire in the wall, it got compromised some how when the patched wall..?
not so fast.
I have an old kenwood preamp and adcom 2 channel. I hook up "bad wires" in wall directly to kenwood and the speaker works fine. how can bad wire short one amp and work on another???

So then I hook up an RCA pre out channel from the onkyo to the adcom and the same very loud buzz comes on the good speakers.

So the Pre outs on the Onkyo are definitely sending the buzz to both amps... can we assume the Onkyo pre outs are shot.
Million dollar question. Why does the line in the wall short out the onkyo but work on my old kenwood.

So then I test a good speaker line on each output on the onkyo. They all work... I'm doing this with it on, even though I know better... Then I went to connect the bad wires to the onkyo again and I got a spark when I connected the red wire...I've never seen a speaker wire spark off a preamp????!!!!
i've never seen that. I'm going to get a meter and read the line resistance and see if there is a difference with the bad wire.
My concern... If I go get a new preamp, can the bad speaker wire blow it again.
Makes no sense.
That wire was hooked up through the B&K. B&K was connected via RCAs to Onkyo. How could it short the onkyo going back through the B&K.
do we think the onkyo was toasted in the move. If so, how is it that just that 1 line shorts the onkyo and none of the others... too strange
riasillo
riasillo OP
12 posts
 
so i tested with meter.
I dont have much experience with meters, tested some circuits at first job but it was always under direction.

Both set ups respond the same.
i had to crank up ohm resistance on meter to get a reading. First time around both pinged beyond zero...so cranked up resistance dial so reading was right in the middle on good set up. suspect wire, pinged middle.
both respond identical. the wire must be good...right?

2 settings x1k and x10. both respond same
except at x10 setting I hear static from speakers.
?
all other settings detect nada on either.
too bizare...that just that wire shorts out onkyo..

pre out from onkyo still shot..
off to buy a new receiver... open to other suggestions using meter.... anyone that lives in the Los angeles vetura county area and want a suspect onkyo sr705 to tinker with?
thanks to everyone for help
theo's avatar
theo
2,684 posts
 
At this point I would check for the short. Use the "Ohm" section of your meter. This checks for continuity, (briefly: the completion of path of the signal/current between two points)and will confirm if you do or don't have a short. Since you know that your speakerwire in the wall is/was insulated between the negative and positive lead. It should not give you a reading on your Ohm Meter if you touch your meter leads to the both connectors at either end of your speakerwire run.
Don't connect your new receiver to anything till you confirm if you do or don't have a short.
riasillo OP
12 posts
 
when i test the wires they read no resistance.
dial swings from infinity all the way to beyod 0 the second i complete the circuit. same as on the non suspect wires...

the wires in the wall are perfect as far as I can tell.

is there any way to test them with my kenwood amp running juice to the speakers so that I can see if under power they have a different reading? or a difference between speakers and wires.
almarg's avatar
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almarg
9,670 posts
 
To check for a short in the wiring you have to disconnect both the speakers and the amplifier, so that the wires are connected to nothing at either end.

Then set the meter to R x 1, and touch the two leads of the meter to each other. There should be a knob on the meter, perhaps on the side, that is called "ohms adjust" or something like that. While the two leads of the meter are touching each other, adjust the knob so that the meter reads 0 ohms.

Then touch one lead of the meter to either the + or the - conductor of one of the speaker wire pairs, and touch the other lead of the meter to the other conductor in that pair. It doesn't matter which end of the cable you do that on. The meter pointer should not move at all, and should indicate approximately infinity ohms, or whatever it indicates when the meter is not connected to anything. (There is probably a separate screw-type adjustment on the meter to set the reading to infinity when it is not connected to anything).

Making a meaningful reading while the speakers are connected can be tricky, and is probably impossible using the R x 1K or R x 10 scales, because on those scales you won't be able to distinguish between the speaker's resistance and a short. Using one of the higher scales, such as R x 1K, also creates the possibility that you are reading your body's resistance, if your fingers are in contact with the metal part of the test leads or the wires when you make the measurement.

Regards,
-- Al
metro04
222 posts
 
It sounds like only *one* of the speaker wire conductors is shorted to house/earth ground within the wall (either conductor) and would cause the problems he's describing depending how his amps are configured. Note how the Kenwood works fine on the suspect wires. This grounding issue could affect other components feeding the amp via the interconnects and shared AC grounding, thus potentially shorting input circuits.

If the speaker cables were terminated in metal wall boxes (or not), disconnect the speakers and amp from the wires, connect your meter to one of wire conductors and the other meter lead to the nearest AC out metal cover screw, or the outlet's "ground" contact. Note any meter shorting, then try the wire's other conductor to outlet's "ground" conductor. If wall outlets are to far away, use a 3-prong extension cord and repeat the steps above to the cord's "ground", or any other grounded metal piping or electrical conduit.
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